Non-invasive measurement of blood oxygen saturation

Abstract

The invention relates to a method for non-invasive determination of oxygen saturation of blood within a deep vascular structure of a human patient comprising locating on skin of the patient in a vicinity of the deep vascular structure of interest emitter and receiver elements of a light oximeter device, wherein optimal location of said elements is achieved through matching of a plethysmography trace obtained from the oximeter device to known plethysmography characteristics of the deep vascular structure of interest, and wherein oxygen saturation is determined from a ratio of light absorbed at different wavelengths by haemoglobin in the blood within the vascular structure of interest. The invention also relates to modified oximetry devices capable of carrying out the method.

The invention claimed is: 
     
       1. A method for non-invasive determination of oxygen saturation of central venous or mixed venous blood within a deep vascular structure of interest in a human patient that contains central venous or mixed venous blood, the method comprising:
 placing emitter and receiver elements of a light oximeter device on the patient's skin in the vicinity of the deep vascular structure of interest wherein the deep vascular structure contains central venous or mixed venous blood, further wherein placement of said elements is achieved through matching of a plethysmography trace obtained from the oximeter device to known plethysmography characteristics of the deep vascular structure of interest; and 
 determining oxygen saturation of blood within the deep vascular structure of interest, wherein oxygen saturation is determined from a ratio of light absorbed at different wavelengths by haemoglobin in the blood within the deep vascular structure of interest. 
 
     
     
       2. The method of  claim 1  wherein the step of determining oxygen saturation comprises determining central venous blood oxygen saturation. 
     
     
       3. The method of  claim 2  wherein the deep vascular structure of interest is selected from the internal jugular vein, subclavian vein, femoral vein, brachiocephalic vein, inferior vena cava, superior vena cava and right atrium. 
     
     
       4. The method of  claim 1  wherein the step of determining oxygen saturation comprises determining mixed venous blood oxygen saturation. 
     
     
       5. The method of  claim 4  wherein the deep vascular structure of interest is selected from the right ventricle and pulmonary artery. 
     
     
       6. The method of  claim 1  further comprising emitting light from the emitter element in both red and infra-red wavelengths. 
     
     
       7. The method of  claim 6  wherein the red light has a wavelength of between about 620 nm and about 750 nm. 
     
     
       8. The method of  claim 6  wherein the red light has a wavelength of between about 640 nm and about 680 nm. 
     
     
       9. The method of  claim 6  wherein the red light has a wavelength of about 660 nm. 
     
     
       10. The method of  claim 6  wherein the infra-red light has a wavelength of between about 750 nm and about 1 mm. 
     
     
       11. The method of  claim 6  wherein the infra-red light has a wavelength of between about 900 nm and about 960 nm. 
     
     
       12. The method of  claim 6  wherein the infra-red light has a wavelength of about 905 nm, 910 nm or 940 nm. 
     
     
       13. An oximetry device configured for use in the method of  claim 1 . 
     
     
       14. An oximetry device comprising:
 a central processing unit, 
 a display; and 
 emitter and receiver elements adapted for releasable application to human skin, wherein the emitter elements are configured to emit light of both red and infra-red wavelengths and the receiver elements are configured to detect said light, and to transmit information relating to levels of emitted and received light to said central processing unit; 
 wherein said central processing unit is configured to match plethysmography characteristics derived from the transmitted information relating to levels of emitted and received light with predetermined plethysmography characteristics of a deep vascular structure of interest that contains central venous or mixed venous blood, to ensure positioning of the emitter and receiver elements on the skin in a vicinity of the deep vascular structure of interest; said central processing unit also being configured to derive a measurement of blood oxygen saturation within the deep vascular structure of interest from the information relating to levels of emitted and received light, for display; 
 wherein the central processing unit, display and emitter and receiver elements are workably connected in use. 
 
     
     
       15. The oximetry device according to  claim 14  wherein the device is configured so that the plethysmography characteristics of the deep vascular structure of interest can be made available on the display. 
     
     
       16. The oximetry device of  claim 14  wherein the workable connection is physical. 
     
     
       17. The oximetry device of  claim 14  wherein the workable connection is wireless. 
     
     
       18. The oximetry device of  claim 14  wherein the emitter elements are configured to emit red light at a wavelength of between about 640 nm and about 680 nm. 
     
     
       19. The oximetry device of  claim 14  wherein the emitter elements are configured to emit infra-red light at a wavelength of between about 900 nm and about 960 nm.